Why does everyone seem to think that a currency has to be constantly depreciating to be used as a currency?

1. Hold on to only as much Fiat as you need to in order to satisfy your needs for emergency funds or planned long term diversification strategy. This can be literally anywhere from 0% to 100% of your networth depending on your plan.
2. Anything that does not fall under #1 or other diversified investments, buy cryptocurrencies (convert at the time when you are paid in dollars, or just get paid in crypto). It is in your best interest to do this conversion immediately upon receipt of extra dollars (not in #1), because by the time you wish to spend on something, your crypto is more likely to have gone up in purchasing power, and your dollars are more likely to have gone down in purchasing power.
3. When you wish to spend on something, you will not spend dollars because all of your dollars are allocated towards purpose of #1 which you have already set aside. Therefore you will spend your crypto. On top of that, if the value of the crypto went way up then spending it on goods and services helps to rebalance your asset allocation. On the flip side, spend dollars if the crypto value has gone down until you are rebalanced.

Why does everyone seem to think that a currency has to be constantly depreciating to be used as a currency?

1. Hold on to only as much Fiat as you need to in order to satisfy your needs for emergency funds or planned long term diversification strategy. This can be literally anywhere from 0% to 100% of your networth depending on your plan.
2. Anything that does not fall under #1 or other diversified investments, buy cryptocurrencies (convert at the time when you are paid in dollars, or just get paid in crypto). It is in your best interest to do this conversion immediately upon receipt of extra dollars (not in #1), because by the time you wish to spend on something, your crypto is more likely to have gone up in purchasing power, and your dollars are more likely to have gone down in purchasing power.
3. When you wish to spend on something, you will not spend dollars because all of your dollars are allocated towards purpose of #1 which you have already set aside. Therefore you will spend your crypto. On top of that, if the value of the crypto went way up then spending it on goods and services helps to rebalance your asset allocation. On the flip side, spend dollars if the crypto value has gone down until you are rebalanced.

Why are you advocating for buying cryptos rather than, say, real estate?